Recent years have seen increasing high performance in electronic devices such as mobile information devices and information appliances following the development of digital technology. With the increased high performance in these electronic devices, miniaturization and increase in speed of semiconductor memory devices used are rapidly advancing. In particular, application of semiconductor memory devices to large-capacity nonvolatile memories, typified by flash memory, is expanding at a rapid pace. Additionally, as next-generation new nonvolatile memories having a potential to replace flash memory, a resistive random access memory (ReRAM) using variable resistance elements has been researched and developed.
Here, variable resistance element refers to an element which has a property in which a resistance state (resistance value) reversibly changes according to an electrical signal, and is capable of maintaining a resistance state. The variable resistance element is capable of storing information in a nonvolatile manner by allocating information to each resistance state. More specifically, it is possible to store two values by allocating a value of 0 to one of a low resistance state in which the resistance value is relatively low and a high resistance state in which the resistance value is higher than the low resistance state, and a value of 1 to the other, for example.
A conventional variable resistance element includes a variable resistance layer, in which two variable resistance materials having different degrees of oxygen deficiency are stacked, is formed between a first electrode and a second electrode. Applying an electric pulse (for example, a voltage pulse) between the first electrode and the second electrode of the variable resistance element causes the resistance state to change from a high resistance state to a low resistance state, or from a low resistance state to a high resistance state.
In this type of variable resistance memory, it is preferable that the two values assigned to the low and high resistance states can be definitively distinguished, and that the change between the low resistance state and the high resistance state occur in a rapid and stable manner.
As one example of such a variable resistance element, a nonvolatile memory device including a first electrode, a variable resistance layer configured of a transition metal oxide stacked structure, and a second electrode has been proposed (for example, see Patent Literature (PTL) 1). For example, Patent Literature (PTL) 1 discloses that variation in resistance is stabilized by causing oxidation-reduction reactions to occur at the electrode interface in contact with the variable resistance region high in oxygen content atomic percentage.